We recently documented the changing patterns of antibiotic resistance in various strains of Streptococcus isolated from patients with active periodontal disease during their course of tetracycline therapy. Some of these streptococci contained extrachromosomal genetic material (plasmids) with characteristics similar to the tetracycline resistance plasmid found in other streptococci. The detection of a single plasmid of identical molecular weight in three distinct streptococcal species isolated from the same patient on different occasions suggested a common origin for this plasmid and indicated that natural transfer of plasmid DNA among the oral streptocci is possible. I now seek evidence to support an association between these plasmids and tetracycline resistance by using methods or agents which cure cells of plasmids, and whether the plasmids are truly identical by employing a series of restriction endonucleases. Many plasmids are self-transmissible my mediating their own transfer to another cell via cell-to-cell contact. Plasmids code for many functions such as inactivating an antibiotic by chemical modification resulting in an antibiotic resistant cell. Rapid dissemination of this plasmid among cells subsequently results in the emergence of an antibiotic resistant cell population. We recently reported the cell-to-cell ("conjugal") transfer of plasmid-coded erythromycin resistance among strains of oral streptococci isolated from periodontal patients. I seek to determine the transmissibility of the putative tetracycline plasmid by applying this plasmid-transfer model and also a transformation model. These studies will provide evidence for the mechanism(s) involved in plasmid transfer among oral streptococci. Molecular analyses of the plasmid(s) within donor and plasmid-recipient cells will reveal plasmid stability, incompatibility, and/or alterations. Familiarization with the basic mechanism(s) involved in the natural transfer of antibiotic resistance among oral streptococci will provide a foundation for the prudent use of these antibiotics in the treatment of periodontal disease while maintaining antibiotic efficacy.